1. Field of the Invention
This invention relates to apparatus and methods for controlling the display of a digital image. The present invention is particularly useful for quickly and efficiently reversing and/or rotating images for a computer display or printer.
2. Description of the Related Art
Methods for processing digital imagery in computers tend to be slow because of the number of steps and the amount of memory involved. Any method which shaves even a small amount of time off of a step which is repeated many times will result in a performance improvement.
Previously, if a section of an image was to be reversed (the last pixel exchanged with the first pixel and so on through the section), a look up table was used. An example of this method is given in U.S. Pat. No. 4,947,344 by Hayashi et al. It is necessary to reverse many small sections of an image in order to rotate it 180 degrees about a central point, or to get its mirror image. Thus, an improvement in the time to reverse a section of an image results in better performance overall.
Attempts have been made to improve the performance of rotating an image 90 degrees. IBM TECHNICAL DISCLOSURE BULLETIN Vol. 27, no. 8, January 1985, pp 4593-4595 by G. Goertzel gives one example. Another example of rotating images 90 degrees and 270 degrees is given in IBM TECHNICAL DISCLOSURE BULLETIN Volume 30, number 12, May 1988, pp 26-28 by C. Cox.
A need remains in the art for a faster method of reversing a section of an image.